Reduction of feature critical dimensions

ABSTRACT

A feature in a layer is provided. A photoresist layer is formed over the layer. The photoresist layer is patterned to form photoresist features with photoresist sidewalls, where the photoresist features have a first critical dimension. A conformal layer is deposited over the sidewalls of the photoresist features to reduce the critical dimensions of the photoresist features. Features are etched into the layer, wherein the layer features have a second critical dimension, which is less than the first critical dimension.

RELATED APPLICATIONS

This application is a continuation of prior U.S. patent application Ser.No. 10/648,953 , entitled “Reduction of Feature Critical Dimensions”,filed on Aug. 26, 2003, now U.S. Pat. No. 7,250,371 by inventors Kang etal., which is incorporated herein by reference and from which priorityunder 35 U.S.C. § 120 is claimed.

BACKGROUND OF THE INVENTION

The present invention relates to the formation of semiconductor devices.

During semiconductor wafer processing, features of the semiconductordevice are defined in the wafer using well-known patterning and etchingprocesses. In these processes, a photoresist (PR) material is depositedon the wafer and then is exposed to light filtered by a reticle. Thereticle is generally a glass plate that is patterned with exemplaryfeature geometries that block light from propagating through thereticle.

After passing through the reticle, the light contacts the surface of thephotoresist material. The light changes the chemical composition of thephotoresist material such that a developer can remove a portion of thephotoresist material. In the case of positive photoresist materials, theexposed regions are removed, and in the case of negative photoresistmaterials, the unexposed regions are removed. Thereafter, the wafer isetched to remove the underlying material from the areas that are nolonger protected by the photoresist material, and thereby define thedesired features in the wafer.

Various generations of photoresist are known. Deep ultra violet (DUV)photoresist is exposed by 248 nm light. To facilitate understanding,FIG. 1A is a schematic cross-sectional view of a layer 108 over asubstrate 104, with a patterned photoresist layer 112, over an ARL(Anti-reflective layer) 110 over the layer 108 to be etched forming astack 100. The photoresist pattern has a critical dimension (CD), whichmay be the width 116 of the smallest feature. Presently, for 248 nmphotoresist a typical CD for the photoresist may be 230-250 nm usingconventional processes. Due to optical properties dependent onwavelength, photoresist exposed by longer wavelength light has largertheoretical minimal critical dimensions.

A feature 120 may then be etched through the photoresist pattern, asshown in FIG. 1B. Ideally, the CD of the feature (the width of thefeature) is equal to the CD 116 of the feature in the photoresist 112.In practice, the CD of the feature 116 may be larger than the CD of thephotoresist 112 due to faceting, erosion of the photoresist, orundercutting. The feature may also be tapered, where the CD of thefeature is at least as great as the CD of the photoresist, but where thefeature tapers to have a smaller width near the feature bottom. Suchtapering may provide unreliable features.

In order to provide features with smaller CD, features formed usingshorter wavelength light are being pursued. 193 nm photoresist isexposed by 193 nm light. Using phase shift reticles and othertechnology, a 90-100 nm CD photoresist pattern may be formed, using 193nm photoresist. This would be able to provide a feature with a CD of90-100 nm. 157 nm photoresist is exposed by 157 nm light. Using phaseshift reticles and other technology sub 90 nm CD photoresist patternsmay be formed. This would be able to provide a feature with a sub 90 nmCD.

The use of shorter wavelength photoresists may provide additionalproblems over photoresists using longer wavelengths. To obtain CD'sclose to the theoretical limit the lithography apparatus should be moreprecise, which would require more expensive lithography equipment.Presently 193 nm photoresist and 157 nm photoresist may not haveselectivities as high as longer wavelength photoresists and may moreeasily deform under plasma etch conditions.

In the etching of conductive layers, such as in the formation of memorydevices, it is desirable to increase device density without diminishingperformance.

SUMMARY OF THE INVENTION

To achieve the foregoing and in accordance with the purpose of thepresent invention a method for forming a feature in a layer is provided.A photoresist layer is formed over the layer. The photoresist layer ispatterned to form photoresist features with photoresist sidewalls, wherethe photoresist features have a first critical dimension. A conformallayer is deposited over the sidewalls of the photoresist features toreduce the critical dimensions of the photoresist features. Features areetched into the layer, wherein the layer features have a second criticaldimension, which is less than the first critical dimension.

In another embodiment of the invention, a method for forming a featurein a layer is provided. A photoresist layer is formed over the layer.The photoresist layer is patterned to form photoresist features withphotoresist sidewalls, where the photoresist features have a firstcritical dimension. A layer is deposited over the sidewalls of thephotoresist features to reduce the critical dimensions of thephotoresist features. The depositing the layer over the sidewalls of thephotoresist feature, comprises, a first deposition with a first gaschemistry to form a first deposition plasma, and a second depositionwith a second gas chemistry to form a second deposition plasma, whereinthe first gas chemistry is different than the second gas chemistry.Features are etched into the layer, wherein the layer features have asecond critical dimension, wherein the second critical dimension is notgreater than 70% of the first critical dimension.

In another embodiment of the invention an apparatus for forming afeature in a layer, wherein the layer is supported by a substrate andwherein the layer is covered by a photoresist mask with photoresistfeatures with a first CD is provided. A plasma processing chamber,comprises a chamber wall forming a plasma processing chamber enclosure,a substrate support for supporting a substrate within the plasmaprocessing chamber enclosure, a pressure regulator for regulating thepressure in the plasma processing chamber enclosure, at least oneelectrode for providing power to the plasma processing chamber enclosurefor sustaining a plasma, a gas inlet for providing gas into the plasmaprocessing chamber enclosure, and a gas outlet for exhausting gas fromthe plasma processing chamber enclosure. A gas source in fluidconnection with the gas inlet comprises a first deposition gas source, asecond deposition gas source, and an etchant gas source. A controllercontrollably connected to the gas source and the at least one electrodecomprises at least one processor and computer readable media. Thecomputer readable media comprises computer readable code for providingat least three deposition cycles to form a sidewall deposition on aphotoresist mask to form features with a second CD, within thephotoresist features, computer readable code for providing a flow of anetchant gas from the etchant gas source to the plasma processing chamberafter completion of the at least three deposition cycles, and computerreadable code for etching features in the layer, using the etchant gaswherein the features in the layer have a third CD. The computer code forproviding at least three deposition cycles to form a sidewall depositionon a photoresist mask to form features with a second CD within thephotoresist features comprises computer readable code for providing aflow of a first deposition gas from the first deposition gas source tothe plasma processing chamber enclosure, computer readable code forstopping the flow of the first deposition gas from the first depositiongas source to the plasma processing chamber enclosure, computer readablecode for providing a flow of a second deposition gas from the seconddeposition gas source to the plasma processing chamber enclosure afterthe flow of the first deposition gas is stopped, and computer readablecode for stopping the flow of the second deposition gas from the seconddeposition gas source to the plasma processing chamber enclosure.

In another embodiment of the invention a method of forming a pluralityof conductive lines is provided. A conductive layer is placed over asubstrate. A mask is formed, where the mask defines a plurality of masklines with mask spaces between the mask lines, where the mask spaceshave a width and wherein the mask lines have a width and have sidewalls.A conformal layer is deposited over the sidewalls of the mask. Theconductive layer is etched through the mask to form conductive lines andspaces between the conductive lines, where the conductive lines have awidth and the spaces between the conductive line have widths, where thewidths of the spaces between the conductive lines is less than thewidths of the mask spaces, and where the widths of the conductive linesis greater than the widths of the line masks.

These and other features of the present invention will be described inmore detail below in the detailed description of the invention and inconjunction with the following figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings and in whichlike reference numerals refer to similar elements and in which:

FIGS. 1A-B are schematic cross-sectional views of a stack etchedaccording to the prior art.

FIG. 2 is a high level flow chart of a process that may be used in anembodiment of the invention.

FIGS. 3A-D are schematic cross-sectional views of a stack processedaccording to an embodiment of the invention.

FIG. 4 is a more detailed flow chart of the step of depositing a layerover sidewalls of photoresist features to reduce CD.

FIG. 5 is a schematic view of a plasma processing chamber that may beused in practicing the invention.

FIG. 6 is a schematic cross-sectional view of a deposition layer whereonly a first deposition phase deposition is used for an entiredeposition layer.

FIG. 7 is a schematic cross-sectional view of a deposition layer whereonly the second deposition phase deposition is used for an entiredeposition layer.

FIG. 8 is a top view of a photoresist etch mask using 248 nmphotoresist.

FIG. 9 is a top view of a deposition layer that has been deposited overthe photoresist etch mask.

FIG. 10 is a cross-sectional view of a feature in a photoresist maskcovered with a deposition layer.

FIGS. 11A-B illustrate a computer system, which is suitable forimplementing a controller used in embodiments of the present invention.

FIG. 12 is a cross-sectional view of a feature in a photoresist maskformed using a 248 nm photoresist.

FIG. 13 is a cross-sectional view of the feature in the photoresist maskcovered with a deposition layer.

FIG. 14 is a cross-sectional view of a feature etched into the layerbelow the photoresist through the feature in the deposition layer, afterthe deposition layer and photoresist layer has been stripped.

FIGS. 15 A-C are cross-sectional views of photoresist masks forproducing conductive lines, according to the prior art.

FIGS. 16A-E are schematic cross-sectional views of a conductive layerprocessed according to an embodiment of the invention.

FIG. 17 is a flow chart of an etch step.

FIGS. 18A-D are schematic cross-sectional views of a conductive layerprocessed according to an embodiment of the invention.

FIG. 19 is a schematic illustration of a device that may be used forpracticing the invention for etching conductive layers.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described in detail with reference toa few preferred embodiments thereof as illustrated in the accompanyingdrawings. In the following description, numerous specific details areset forth in order to provide a thorough understanding of the presentinvention. It will be apparent, however, to one skilled in the art, thatthe present invention may be practiced without some or all of thesespecific details. In other instances, well known process steps and/orstructures have not been described in detail in order to notunnecessarily obscure the present invention.

The invention provides features with small critical dimensions (CD).More specifically, the invention provides a features with CD's that areless than the CD of the photoresist pattern used to etch the feature.

To facilitate understanding, FIG. 2 is a high level flow chart of aprocess that may be used in an embodiment of the invention. A patternedphotoresist mask is provided (step 204). FIG. 3A is a schematiccross-sectional view of a layer to be etched 308 over a substrate 304,with a patterned photoresist mask 312 with a feature 314, over a ARL310, over the layer 308 to be etched forming a stack 300. Thephotoresist mask has a photoresist feature critical dimension (CD),which may be the widest part of the width 316 of the smallest possiblefeature. Presently, for 248 nm photoresist a typical CD for thephotoresist may be 230-250 nm, using conventional processes.

A layer is then deposited over the sidewalls of the photoresist featuresto reduced the CD (step 208). FIG. 3B is a schematic cross-sectionalview of the patterned photoresist mask 312 with a layer 320 depositedover the sidewalls of the feature 314. The deposited layer 320 forms adeposited layer feature 322 within the photoresist feature 314, wherethe deposited layer feature 322 has a reduced CD 324 that is less thanthe CD 316 of the photoresist feature 314. Preferably, the reduced CD324 of the deposited layer feature 322 is at least 30% less than the CD316 of the photoresist feature (i.e. not greater than 70% of the CD 316of the photoresist feature). More preferably, the reduced CD 324 of thedeposited layer feature 322 is at least 40% less than the CD 316 of thephotoresist feature (i.e. not greater than 60% of the CD 316 of thephotoresist feature). Most. preferably, the reduced CD 324 of thedeposited layer feature 322 is at least 50% less than the CD 316 of thephotoresist feature (i.e. not greater than 50% of the CD 316 of thephotoresist feature). For example, the deposited layer feature may havea reduced CD 316 that is 99% less than the CD 316 of the photoresistfeature. It is also desirable that the deposited layer feature 322 hassubstantially vertical sidewalls 328, which are highly conformal asshown. An example of a substantially vertical sidewall is a sidewallthat from bottom to top makes an angle of between 88° to 90° with thebottom of the feature. Conformal sidewalls have a deposition layer thathas substantially the same thickness from the top to the bottom of thefeature. Non-conformal sidewalls may form a faceting or a bread-loafingformation, which provide non-substantially vertical sidewalls. Taperedsidewalls (from the faceting formation) or bread-loafing sidewalls mayincrease the deposited layer CD and provide a poor etching mask.Preferably, the deposition on the side wall is thicker than thedeposition on the bottom of the photoresist feature. More preferably, nolayer is deposited over the bottom of the photoresist feature.

Features are then etched into the layer to be etched 308 through thedeposited layer features 322 (step 212). FIG. 3C shows a feature 332etched into the layer to be etched 308. In this example, the feature 332etched in the layer to be etched 308 has a CD 336, which is equal to theCD 324 of the deposited layer feature 322. In practice, the CD 336 ofthe feature 332 may be slightly larger than the CD 324 of the feature322 of the deposited layer 320. However, since the CD 324 of thedeposited layer feature 322 is significantly smaller than the CD 316 ofthe photoresist 312, the CD 336 of the feature 332 in the layer to beetched 308 is still smaller than the CD 316 of the photoresist 312. Ifthe CD 324 of the deposited layer was only slightly smaller than the CDof the photoresist, or if the deposited layer was faceted or breadloafed, then the CD of the layer to be etched might not be smaller thanthe CD of the photoresist. In addition, a faceted or bread-loafingdeposited layer may cause a faceted or irregularly shaped feature in thelayer to be etched. It is also desirable to minimize deposition on thebottom of the photoresist feature. Preferably, the CD 336 of the feature332 etched in the layer to be etched 308 is at least 30% less than theCD 316 of the photoresist feature. More preferably, the CD 336 of thefeature 332 etched in the layer to be etched 308 is at least 40% lessthan the CD 316 of the photoresist feature. Most preferably, the CD 336of the feature 332 etched in the layer to be etched 308 is at least 50%less than the CD 316 of the photoresist feature.

The photoresist and deposited layer may then be stripped (step 216).This may be done as a single step or two separate steps with a separatedeposited layer removal step and photoresist strip step. Ashing may beused for the stripping process. FIG. 3D shows the stack 300 after thedeposited layer and photoresist mask have been removed. Additionalformation steps may be performed (step 220). For example, a contact 340may then be formed in the feature. To provide a dual damascenestructure, a trench may be etched before the contact is formed.Additional processes may be performed after the contact is formed.

FIG. 4 is a more detailed flow chart of the deposit layer over sidewallsof photoresist features to reduce CD step 208. In the embodiment, thedeposit layer over sidewalls of photoresist features to reduce CD step208 comprises a first deposition phase 404 and a second deposition phase408.

EXAMPLE OF DIELECTRIC ETCH

FIG. 5 is a schematic view of a plasma processing chamber 500 that maybe used for depositing the layer, etching, and stripping. The plasmaprocessing chamber 500 comprises confinement rings 502, an upperelectrode 504, a lower electrode 508, a gas source 510, and an exhaustpump 520. The gas source 510 comprises a first deposition gas source 512and a second deposition gas source 516. The gas source 510 may compriseadditional gas sources, such as an etching gas source 518. Within plasmaprocessing chamber 500, the substrate 304 is positioned upon the lowerelectrode 508. The lower electrode 508 incorporates a suitable substratechucking mechanism (e.g., electrostatic, mechanical clamping, or thelike) for holding the substrate 304. The reactor top 528 incorporatesthe upper electrode 504 disposed immediately opposite the lowerelectrode 508. The upper electrode 504, lower electrode 508, andconfinement rings 502 define the confined plasma volume. Gas is suppliedto the confined plasma volume by the gas source 510 and is exhaustedfrom the confined plasma volume through the confinement rings 502 and anexhaust port by the exhaust pump 520. A first RF source 544 iselectrically connected to the upper electrode 504. A second RF source548 is electrically connected to the lower electrode 508. Chamber walls552 surround the confinement rings 502, the upper electrode 504, and thelower electrode 508. Both the first RF source 544 and the second RFsource 548 may comprise a 27 MHz power source and a 2 MHz power source.Different combinations of connecting RF power to the electrode arepossible. In the case of Exelan HPT™, which is basically the same as anExelan HP with a Turbo Pump attached to the chamber, made by LAMResearch Corporation™ of Fremont, Calif., which may be used in apreferred embodiment of the invention, both the 27 MHz and 2 MHz powersources make up the second RF power source 548 connected to the lowerelectrode, and the upper electrode is grounded. A controller 535 iscontrollably connected to the RF sources 544, 548, exhaust pump 520, andthe gas source 510. The Exelan HPT would be used when the layer to beetched 308 is a dielectric layer, such as silicon oxide or organosilicate glass.

FIGS. 11A and 11B illustrate a computer system 1300, which is suitablefor implementing a controller 535 used in embodiments of the presentinvention. FIG. 11A shows one possible physical form of the computersystem. Of course, the computer system may have many physical formsranging from an integrated circuit, a printed circuit board, and a smallhandheld device up to a huge super computer. Computer system 1300includes a monitor 1302, a display 1304, a housing 1306, a disk drive1308, a keyboard 1310, and a mouse 1312. Disk 1314 is acomputer-readable medium used to transfer data to and from computersystem 1300.

FIG. 11B is an example of a block diagram for computer system 1300.Attached to system bus 1320 is a wide variety of subsystems.Processor(s) 1322 (also referred to as central processing units, orCPUs) are coupled to storage devices, including memory 1324. Memory 1324includes random access memory (RAM) and read-only memory (ROM). As iswell known in the art, ROM acts to transfer data and instructionsuni-directionally to the CPU and RAM is used typically to transfer dataand instructions in a bi-directional manner. Both of these types ofmemories may include any suitable of the computer-readable mediadescribed below. A fixed disk 1326 is also coupled bi-directionally toCPU 1322; it provides additional data storage capacity and may alsoinclude any of the computer-readable media described below. Fixed disk1326 may be used to store programs, data, and the like and is typicallya secondary storage medium (such as a hard disk) that is slower thanprimary storage. It will be appreciated that the information retainedwithin fixed disk 1326 may, in appropriate cases, be incorporated instandard fashion as virtual memory in memory 1324. Removable disk 1314may take the form of any of the computer-readable media described below.

CPU 1322 is also coupled to a variety of input/output devices, such asdisplay 1304, keyboard 1310, mouse 1312 and speakers 1330. In general,an input/output device may be any of: video displays, track balls, mice,keyboards, microphones, touch-sensitive displays, transducer cardreaders, magnetic or paper tape readers, tablets, styluses, voice orhandwriting recognizers, biometrics readers, or other computers. CPU1322 optionally may be coupled to another computer or telecommunicationsnetwork using network interface 1340. With such a network interface, itis contemplated that the CPU might receive information from the network,or might output information to the network in the course of performingthe above-described method steps. Furthermore, method embodiments of thepresent invention may execute solely upon CPU 1322 or may execute over anetwork such as the Internet in conjunction with a remote CPU thatshares a portion of the processing.

In addition, embodiments of the present invention further relate tocomputer storage products with a computer-readable medium that havecomputer code thereon for performing various computer-implementedoperations. The media and computer code may be those specially designedand constructed for the purposes of the present invention, or they maybe of the kind well known and available to those having skill in thecomputer software arts. Examples of computer-readable media include, butare not limited to: magnetic media such as hard disks, floppy disks, andmagnetic tape; optical media such as CD-ROMs and holographic devices;magneto-optical media such as floptical disks; and hardware devices thatare specially configured to store and execute program code, such asapplication-specific integrated circuits (ASICs), programmable logicdevices (PLDs) and ROM and RAM devices. Examples of computer codeinclude machine code, such as produced by a compiler, and filescontaining higher level code that are executed by a computer using aninterpreter. Computer readable media may also be computer codetransmitted by a computer data signal embodied in a carrier wave andrepresenting a sequence of instructions that are executable by aprocessor.

Other examples may use other deposition devices.

One example of a first deposition phase 404 may be CH₃F deposition usinga chemistry of 250 sccm (standard cubic centimeters per minute) Ar and50 sccm CH₃F, at a pressure of 60 mTorr, established by setting a Vatvalve of the turbo pump to 1000. The 27 MHz RF source provides 500 Wattsof power, while the 2 MHz RF source provides 100 Watts of power. Thechamber temperature is maintained at 20° C. A helium cooling pressure,to cool the substrate is 15 Torr.

One example of a second deposition phase 408 may be C₄F₆/O₂/COdeposition using a chemistry of 270 sccm Ar, 12 sccm C₄F₆, 8 sccm O₂,and 100 sccm CO, at a pressure of 50 mTorr, established by setting a Vatvalve of the turbo pump to 1000. The 27 MHz RF source provides 1500Watts of power, while the 2 MHz RF source provides 480 Watts of power.The chamber temperature is maintained at 20° C. A helium coolingpressure, to cool the substrate is 15 Torr.

FIG. 6 is a schematic cross-sectional view of a deposition layer 620where only the first deposition phase deposition is used for an entiredeposition layer 620. The deposition layer 620 is formed over aphotoresist mask 612, over an ARL 610, over a layer to be etched 608,over a substrate 604. The photoresist mask 612 forms a feature 614. Inthis example, the first deposition forms a “bread-loafing” depositionlayer. The bread-loafing deposition layer is characterized by a thickersidewall deposition 632 near the top of the feature and a thinner (orno) sidewall deposition 636 near the bottom of the feature. Therefore,this deposition provides a non-conformal sidewall deposition. Such adeposition does not provide the desired substantially verticalsidewalls. The bread-loafing eventually pinches off the top, which thencannot be used as a masking layer, since the contact will be closed offand no etching can be done.

FIG. 7 is a schematic cross-sectional view of a deposition layer 720where only the second deposition phase deposition is used for an entiredeposition layer 720. The deposition layer 720 is formed over aphotoresist mask 712, over an ARL 710, over a layer to be etched 708,over a substrate 704. The photoresist mask 712 forms a feature 714. Inthis example, the first deposition forms a “faceting” deposition layer.The faceting deposition layer is characterized by a thinner (or no)sidewall deposition 732 near the top of the feature and a thickersidewall deposition 736 near the bottom of the feature. Therefore, thisdeposition also provides a non-conformal sidewall deposition. If thesidewalls near the top are too thin, faceting 740 of the photoresistmask 712 may result. Such a deposition does not provide the desiredsubstantially vertical sidewalls. The faceting of the corners of thephotoresist mask may cause lower etch selectivity and fast mask erosion.The faceting of the mask will also result in faceting of the etchedprofile. In almost all cases, once the mask is faceted, then the finaletched profile is also faceted, since the mask vertical profilegenerally translates into the etched material.

Therefore in an example of a preferred embodiment of the invention, thefirst deposition phase 404 and the second deposition phase 408 in theexample above are alternated for 6 cycles, where the first depositionphase 404 is for 2 seconds and the second deposition phase 408 is for 25seconds. Such a deposition would have a first deposition of the firstdeposition phase 404, and then a second deposition of the seconddeposition phase 408, then a third deposition of the first depositionphase 404, then a fourth deposition of the second deposition phase 408,which is repeated until there is a twelfth deposition.

FIG. 8 is a top view of a photoresist etch mask 804 using 248 nmphotoresist. The photoresist etch mask 804 has a plurality ofphotoresist features 808. In this example, the photoresist features 808have a CD 812 of 206 nm. In this example, the CD 812 is the diameter ofthe photoresist feature.

FIG. 9 is a top view of a deposition layer 904 that has been depositedover the photoresist etch mask using the above described example. Thedeposition layer 904 has plurality of features 908, located within theplurality of photoresist features. The features 908 have a CD 912 thatwas measured, in this example, to be 115 nm, which is 56% of the CD 812of the photoresist feature, so that the CD 912 of the deposited layerfeature is 44 % less than the CD 812 of the photoresist feature. In thisexample, the CD is the diameter of the feature.

FIG. 10 is a cross-sectional view of a feature 1002 in a photoresistmask 1004 covered with a deposition layer 1008. As shown, the feature1002 has substantially vertical sidewalls 1010, so that the width of thefeature is substantially the same along the length of the feature 1002.In addition, the layer on the sidewalls is highly conformal, so that thelayer has a uniform thickness from the top to the bottom of the feature.

FIG. 12 is a cross-sectional view of a feature 1202 in a photoresistmask 1204 formed using a 248 nm photoresist. In this example thephotoresist feature has a CD of 250 nm. A two phase deposition is usedto provide a deposition layer over the sidewalls of the photoresist mask1204. The two phase deposition may use a different recipe than theprevious example. FIG. 13 is a cross-sectional view of the feature 1202in the photoresist mask 1204 covered with a deposition layer 1208. TheCD of the feature in the deposition layer 1208 is 140 nm. The feature inthe deposition layer 1208 is used to etch a layer below the photoresist.FIG. 14 is a cross-sectional view of a feature 1404 etched into thelayer 1408 below the photoresist through the feature in the depositionlayer, after the deposition layer and photoresist layer has beenstripped. The CD of the feature 1404 is 140 nm.

The ability to control the ratio of etch times of the first depositionphase 404 and the second deposition phase 408 provide another controlvariable. A proper ratio will provide substantially vertical andconformal sidewalls as illustrated in FIG. 3B. Such a deposition layeris also able to protect the photoresist mask to increase etchselectivity. Other control parameters provided by the invention that canbe used to control the deposition profiles are: number of cycles, totaldeposition time, deposition1/deposition2 time ratio, gas chemistry ratio(such as CH₃F/O₂ ratio or C₄F₆/O₂ ratio). Other gas chemistries such asCH₂F₂ instead of CH₃F or C₄F₈ instead of C₄F₆, etc. may be used.

The ability to form features with smaller critical dimensions, withoutchanging the photoresist, allows for smaller features without purchasingnew lithography equipment. In newer generations of photoresist are used,the invention provides small CD's for the newer generations ofphotoresist.

In other embodiments, three or more different gas chemistries may beused providing three or more different deposition phases.

EXAMPLE OF CONDUCTIVE LAYER ETCH

In the formation of conductive lines, such as metal connectors or memorydevices like flash memory, it is desirable to increase the thickness ofthe conductive lines and/or decrease the CD of the spacing between theconductive lines. FIG. 15 A is a cross-sectional view of a photoresistmask for producing conductive lines, when spacing between the lines istoo close according to the prior art. Over a substrate 1504, such as awafer a barrier layer 1506 may be placed. Over the barrier layer 1506 aconductive layer 1508 such as a metal layer or a polysilicon layer isformed. Over the conductive layer 1508 an antireflective layer (ARL)1510 such as a DARC layer is formed. A photoresist mask 1512 is formedover the ARL 1510. In this example, the photoresist mask 1512 forms linemasks 1514 with photoresist residue 1518 formed in spaces between theline masks 1514. The presence of the photoresist residue 1518 is causedby providing too small of a space between the line masks 1514, since itis more difficult to remove residue from a small space. This may limitthe density of the conductive lines that may be provided.

FIG. 15B is another cross-sectional view of a photoresist mask 1512 bfor producing conductive lines, used in the prior art to attempt toovercome the problem created by too small spacing. The line masks 1514 bin this example are made thinner to allow wider spaces 1520 to preventresist residue and maintain the same pitch or density as the previousexample. One of the drawbacks of this approach is that thinner linemasks 1514 b result in thinner lines. The thinner lines may result inless reliability and poorer performance. The thinner lines may result insmaller transistor areas, which may cause a short channel effect andother performance problems, such as short channel effect and highwordline resistance (causing a slower speed)).

FIG. 15C is another cross-sectional view of a photoresist mask 1512 cfor producing conductive lines, used in the prior art to attempt toovercome the problem created by too small spacing. In some applications,it is desirable that the line masks 1514 c have the same width as thespaces 1522. Since in this example, the spaces 1522 are made wider toprevent resist residue, the line masks 1514 c are also wider. As aresult, the pitch is increased and the density of the lines isdecreased.

It is desirable to provide more densely placed conductive lines byreducing spacing between lines while maintaining wider line widths.

The high level process shown in FIG. 2 will be used to facilitate theunderstanding of this embodiment of the invention. A patternedphotoresist mask is provided (step 204). FIG. 16A is a schematiccross-sectional view of a conductive layer to be etched 1608 over abarrier layer 1606 over a substrate 1604, with a patterned photoresistmask 1612 forming mask lines 1614, with mask spaces 1620 therebetween,over an ARL 1610, over the conductive layer 1608 to be etched. Thephotoresist mask has a space critical dimension (CD), which is the width1616 of the space, and a line CD, which is the width 1626 of the masklines 1614. Presently, for 248 nm photoresist a typical CD for the spacewidth CD is 0.16 um. Generally, the width of the space in thephotoresist is made wide enough to provide the formation of the space inthe photoresist without photoresist residue in the space. The width ofthe photoresist mask lines is thin enough to provide an increase densityof conductive lines.

A conformal layer is then deposited over the sidewalls of thephotoresist features to reduced the width of the space (step 208). FIG.16B is a schematic cross-sectional view of the patterned photoresistmask 1612 with a layer 1630 deposited over the sidewalls of the mask1612. The deposited layer 1630 forms a deposited layer space 1632 withinthe mask space, where the deposited layer space 1632 has a reduced width(CD) 1634 that is less than the width 1616 of the mask space. Inaddition, the deposited layer 1630 forms deposited layer mask lines witha width 1638 that is greater than the width 1626 of the mask lines 1614.Preferably, the reduced width 1634 of the deposited layer space 1632 isat least 20% less than the width 1616 of the mask space 1620 (i.e. notgreater than 80% of the width 1616 of the mask space 1620). Morepreferably, the reduced width 1634 of the deposited layer space 1632 isat least 50% less than the width 1616 of the mask space 1620 (i.e. notgreater than 50% of the width 1616 of the mask space 1620). Mostpreferably, the reduced width 1616 of the deposited layer space 1632 isat least 70% less than the width 1634 of the mask space 1620 (i.e. notgreater than 30% of the width 1616 of the mask space 1620). It is alsodesirable that the deposited layer forms substantially verticalsidewalls 1642, which are highly conformal as shown. An example of asubstantially vertical sidewall is a sidewall that from bottom to topmakes an angle of between 88° to 90° with the bottom of the space.Conformal sidewalls have a deposition layer that has substantially thesame thickness from the top to the bottom of the space. This process fora conductive layer etch is able to provide a conformal layer in a singledeposition.

In the preferred embodiment for etching a conductive layer, thedeposition layer is conformal in all directions (isotropic). Thisresults in the layer over the ARL 1610 to be about as thick as the layeron the sidewalls of the mask

The conductive layer 1608 may be etched through the deposited layer 1630(step 212). In this example, the etching step comprises at least twoseparate etches, as illustrated in FIG. 17. An anisotropic depositionlayer etch is used to etch the deposited layer 1630 (step 1704). FIG.16C is a cross-sectional view of the substrate after the deposited layeris anisotropically etched. The remaining deposited layer forms sidewalls1642 around the mask lines 1614. An anisotropic conductive layer etch isused to etch into the conductive layer 1608 (step 1708). FIG. 16D is across-sectional view of the substrate after the conductive layer isetched to form conductive lines 1646 with spaces 1650 formedtherebetween. The conductive lines 1646 have a width 1648 and the spacesbetween the conductive lines have a width 1652, as shown in FIG. 16D.Preferably, the width 1652 of the space 1650 between the conductivelines is at least 20% less than the width 1616 of the space 1620 betweenthe mask lines. More preferably, the width 1652 of the space 1650between the conductive lines is at least 50% less than the width 1616 ofthe space 1620 between the mask lines. Most preferably, the width 1652of the space 1650 between the conductive lines is at least 70% less thanthe width 1616 of the space 1620 between the mask lines.

The photoresist and deposited layer may then be stripped (step 216).This may be done as a single step or two separate steps with a separatedeposited layer removal step and photoresist strip step. Ashing may beused for the stripping process. FIG. 16E shows the stack 1600 after thedeposited layer and photoresist mask have been removed. Additionalprocesses may be performed (step 220). For example, the conductive linesmay be formed to be part of a memory device.

The resulting structure provides a higher density device with smallerspacing and wider conductive lines. In this example, the widths 1648 ofthe conductive lines 1646 are about equal to the widths 1652 of thespaces 1650. Other conductive line width to space width ratios may beprovided by this embodiment. Preferably, the ratio of the width of themask line to the width of the space between mask lines is less than 1:1,where the ratios of the width of the conductive line to the spacebetween the conductive line is not less than 1:1, and even morepreferably greater than 1:1. Such ratios may be useful in providinghigher density memory devices, where the conductive layer is apolysilicon.

In another embodiment of the invention, the mask lines have a width thatis about equal to the width of the space. FIG. 18A is a cross-sectionalview of a conductive layer to be etched 1808 over a barrier layer 1806over a substrate 1804, with a patterned photoresist mask 1812 formingmask lines 1814, with mask spaces 1820 therebetween, over an ARL 1810,over the conductive layer 1808 to be etched. The photoresist mask has aspace critical dimension (CD), which is the width 1816 of the space, anda line CD, which is the width 1826 of the mask lines 1814. Generally,the width of the space in the photoresist is made wide enough to providethe formation of the space in the photoresist without photoresistresidue in the space.

A conformal layer is then deposited over the sidewalls of thephotoresist features to reduced the width of the space (step 208). FIG.18B is a schematic cross-sectional view of the patterned photoresistmask 1812 with a layer 1830 deposited over the sidewalls of the mask1812. The deposited layer 1830 forms a deposited layer space 1832 withinthe mask space, where the deposited layer space 1832 has a reduced width(CD) 1834 that is less than the width 1816 of the mask space. Inaddition, the deposited layer 1830 forms deposited layer mask lines witha width 1838 that is greater than the width 1826 of the mask lines 1814.

The conductive layer 1808 may be etched through the deposited layer 1830(step 212). FIG. 18C is a cross-sectional view of the substrate afterthe conductive layer is etched to form conductive lines 1846 with spaces1850 formed therebetween. The conductive lines 1846 have a width 1848and the spaces between the conductive lines have a width 1852, as shownin FIG. 18C.

The photoresist and deposited layer may then be stripped (step 216).FIG. 18D shows the stack 1800 after the deposited layer and photoresistmask have been removed. Additional processes may be performed (step220). For example, the metal lines may be used for electricallyconnecting various devices.

The resulting structure provides wider conductive wires that are moreclosely spaced. In this example, although the conductive metal lines mayhave the same density as done previously, providing wider conductivelines with smaller spacing improves the performance of the conductivelines, such as by providing a reduced resistance. The inventions mayprovide a conductive line width that is more than 100% greater than theline width of the original mask. More preferably, the conductive linewidth is more than 150% greater than the line width of the originalmask. In this embodiment, the deposition steps are in order and are notsimultaneous.

EXAMPLE RECIPE

In an example recipe, a device that may be used for both depositing andetching the deposition layer and the conductive layer is the 2300Versys™ made by LAM Research Corporation™ of Fremont, Calif. FIG. 19 isa schematic illustration of such a device 1900 used for both depositingand etching the deposition layer. The plasma processing chamber 1900comprises an inductive antenna (or coil) 1902, a gas distribution plate(GDP) 1904, a substrate support 1908, a gas source 1910, and an exhaustpump 1920. The gas source 1910 is in fluid connection with the gasdistribution plate 1904 and comprises a deposition gas source 1912 andan etch gas source 1916. The gas source 1910 may comprise additional gassources, such as a second etching or deposition gas source. Withinplasma processing chamber 1900, the substrate 1604 is positioned uponthe substrate support 1908. The substrate support 1908 incorporates asuitable substrate chucking mechanism (e.g., electrostatic, mechanicalclamping, or the like) for holding the substrate 1604. The reactor top1928 incorporates a quartz dielectric window 1976, which allows thetransmission of energy from the antenna 1902 into the chamber. Thedielectric window 1976, the substrate support 1908, and anodizedaluminum chamber walls 1952 define the confined plasma volume. Gas issupplied to the confined plasma volume by the gas source 1910 and isexhausted from the confined plasma volume through an exhaust port by theexhaust pump 1920. A first RF source 1944 is electrically connected tothe antenna. A second RF source 1948 is electrically connected to thesubstrate support 1908. In this example, the first RF source 1944provides a signal with a 13.56 MHz frequency, and the second RF source1948 provides a signal with a 13.56 MHz frequency.

During the deposition of the deposition layer (step 208), a pressure of10 mTorr is provided to the chamber. The first RF source 1944 provides1000 Watts (TCP power) by the antenna 1902 through the dielectric window1976 into the plasma volume 1940. No bias power is provided to thesubstrate holder 1908. The deposition gas source 1912 provides a flow of50 sccm SiCl₄ and 100 sccm O₂ for a 15 second deposition. This forms a1,000-2,000 Å thick layer of SiCl_(x)O_(y). Such a film may be an oxidefilm, which is strong enough to resist ething.

During the anisotropic etch of the deposition layer (step 1704) apressure of 5 mTorr is provided to the chamber. The first RF source 1994provides 500 Watts by the antenna 1902 to the plasma volume 1940. A biasof −175 volts is applied to the substrate support to accelerate positiveions to the substrate to facilitate etching. The etch gas source 1916provides 100 sccm of CF₄.

The anisotropic etch of the conductive layer (step 1708) is accomplishedusing four etches a BT (breakthrough) etch, an ME1 (main etch 1), ME2(main etch 2), and an OE (over etch). For the BT a 5 mTorr pressure isprovided. 500 Watts are provided through the antenna 1902 to the chamber1900. A bias of −175 volts is applied to the substrate support 1908 toaccelerate ions to the substrate to facilitate etching. The etch sourceprovide 100 sccm of CF₄ for about 10 seconds.

For the ME1 a 10 mTorr pressure is provided. 800 Watts are providedthrough the antenna 1902 to the chamber 1900. A bias of −90 volts isapplied to the substrate support 1908 to accelerate ions to thesubstrate to facilitate etching. The etch source provide 100 sccm ofCl₂, 100 sccm HBr, and 5 sccm O₂ for about 45 seconds.

For the ME2 a 20 mTorr pressure is provided. 400 Watts are providedthrough the antenna 1902 to the chamber 1900. A bias of −170 volts isapplied to the substrate support 1908 to accelerate ions to thesubstrate to facilitate etching. The etch source provide 20 sccm of Cl₂,360 sccm HBr, and 5 sccm O₂. An endpoint detection is used to determinewhen to stop this etch.

For the OE a 60 mTorr pressure is provided. 500 Watts are providedthrough the antenna 1902 to the chamber 1900. A bias of −210 volts isapplied to the substrate support 1908 to accelerate ions to thesubstrate to facilitate etching. The etch source provide 267 sccm of He,133 sccm HBr, and 2 sccm O₂ for about 80 seconds.

Other embodiments may use a hardmask for the mask. In such embodiments,a photoresist mask may be used to open a hardmask. The deposition layermay be placed over the hardmask to reduce the spacing. In thealternative, the deposition layer may be placed over the photoresistbefore etching the hardmask.

While this invention has been described in terms of several preferredembodiments, there are alterations, permutations, and various substituteequivalents, which fall within the scope of this invention. It shouldalso be noted that there are many alternative ways of implementing themethods and apparatuses of the present invention. It is thereforeintended that the following appended claims be interpreted as includingall such alterations, permutations, and various substitute equivalentsas fall within the true spirit and scope of the present invention.

1. A method for forming a feature in a layer, comprising: forming aphotoresist layer over the layer; patterning the photoresist layer toform photoresist features with photoresist sidewalls, where thephotoresist features have a first critical dimension; depositing aconformal layer over the sidewalls of the photoresist features to reducethe critical dimensions of the photoresist features, comprising: a firstdeposition with a first gas chemistry to form a first deposition plasma;comprising: providing a flow of the first deposition gas; forming thefirst deposition gas into a plasma; and stopping the flow of the firstdeposition gas; and a second deposition with a second gas chemistry toform a second deposition plasma, wherein the first gas chemistry isdifferent than the second gas chemistry, comprising: providing a flow ofa second deposition gas different than the first deposition gas; formingthe second deposition gas into a plasma; and stopping the flow of thesecond deposition gas, so that the flow of the first deposition gas andthe flow of the second deposition gas alternates instead of beingsimultaneous; and etching features into the layer, wherein the layerfeatures have a second critical dimension, which is less than the firstcritical dimension.
 2. The method, as recited in claim 1, wherein thedepositing the conformal layer over the photoresist features furthercomprises: a third deposition with the first gas chemistry to form athird deposition plasma; and a fourth deposition with the second gaschemistry to form a fourth deposition plasma.
 3. The method, as recitedin claim 2, wherein the second critical dimension is not greater than70% of the first critical dimension.
 4. The method, as recited in claim3, wherein the depositing the conformal layer over the sidewalls formssubstantially vertical sidewalls.
 5. The method, as recited in claim 4,wherein the photoresist layer is formed from 248 nm photoresist and thefeature has a CD not greater than 140 nm.
 6. The method, as recited inclaim 4, further comprising stripping the photoresist mask and depositedconformal layer with a single stripping step.
 7. The method, as recitedin claim 6, wherein the stripping the photoresist mask and depositedconformal layer comprises ashing the photoresist mask and depositedlayer.
 8. The method, as recited in claim 3, wherein the conformal layerhas a sidewall thickness, wherein the conformal layer has substantiallythe same sidewall thickness from a top to a bottom of the feature. 9.The method, as recited in claim 3, wherein the conformal layer has asidewall thickness and a photoresist feature bottom thickness, whereinthe sidewall thickness is greater than the photoresist feature bottomthickness.
 10. The method, as recited in claim 1, wherein the secondcritical dimension is not greater than 70% of the first criticaldimension.
 11. The method, as recited in claim 1, wherein thephotoresist layer is formed from 248 nm photoresist and the feature hasa CD not greater than 140 nm.
 12. The method, as recited in claim 1,further comprising placing the layer in a plasma processing chamber,wherein the depositing the conformal layer and etching features areperformed in the plasma processing chamber.
 13. The method, as recitedin claim 12, further comprising stripping the conformal layer andphotoresist layer with a single stripping step, while the layer is inthe plasma processing chamber.
 14. The method, as recited in claim 1,wherein the first deposition and second deposition are alternated for atleast 6 cycles.
 15. A method for forming a feature in a layer,comprising: forming a photoresist layer over the layer; patterning thephotoresist layer to form photoresist features with photoresistsidewalls, where the photoresist features have a first criticaldimension; depositing a layer over the sidewalls of the photoresistfeatures to reduce the critical dimensions of the photoresist features,wherein the depositing the layer over the sidewalls of the photoresistfeature, comprises: a first deposition with a first gas chemistry toform a first deposition plasma, comprising: providing a flow of thefirst deposition gas; forming the first deposition gas into a plasma;and stopping the flow of the first deposition gas; and a seconddeposition with a second gas chemistry to form a second depositionplasma, wherein the first gas chemistry is different than the second gaschemistry, comprising: providing a flow of a second deposition gasdifferent than the first deposition gas; forming the second depositiongas into a plasma; and stopping the flow of the second deposition gas,so that the flow of the first deposition gas and the flow of the seconddeposition gas alternates instead of being simultaneous; and etchingfeatures into the layer, wherein the layer features have a secondcritical dimension, wherein the second critical dimension is not greaterthan 70% of the first critical dimension.
 16. The method, as recited inclaim 15, wherein the second critical dimension is not greater than 60%of the first critical dimension.
 17. The method, as recited in claim 15,wherein the depositing the layer over the photoresist features furthercomprises: a third deposition with the first gas chemistry to form athird deposition plasma; and a fourth deposition with the second gaschemistry to form a fourth deposition plasma.
 18. The method, as recitedin claim 17, wherein the depositing the layer over the sidewalls formssubstantially vertical sidewalls.
 19. The method, as recited in claim15, further comprising placing the layer in a plasma processing chamber,wherein the depositing the layer over the sidewalls of the photoresistfeatures and etching features are performed in the plasma processingchamber.
 20. The method, as recited in claim 19, further comprisingstripping the deposited layer and photoresist layer with a singlestripping step, while the layer is in the plasma processing chamber. 21.The method, as recited in claim 15, wherein the first deposition andsecond deposition are alternated for at least 6 cycles.
 22. A method offorming a plurality of conductive lines, comprising: placing aconductive layer over a substrate; forming a mask, wherein the maskdefines a plurality of mask lines with mask spaces between the masklines, wherein the mask spaces have a width and wherein the mask lineshave a width and have sidewalls; placing the substrate in a plasmaprocessing chamber depositing a conformal layer over the sidewalls ofthe mask, while the substrate is in the plasma processing chamber,comprising: a first deposition with a first gas chemistry to form afirst deposition plasma; comprising: providing a flow of the firstdeposition gas; forming the first deposition gas into a plasma; andstopping the flow of the first deposition gas; and a second depositionwith a second gas chemistry to form a second deposition plasma, whereinthe first gas chemistry is different than the second gas chemistry,comprising: providing a flow of a second deposition gas different thanthe first deposition gas; forming the second deposition gas into aplasma; and stopping the flow of the second deposition gas, so that theflow of the first deposition gas and the flow of the second depositiongas alternates instead of being simultaneous; etching the conductivelayer through the mask to form conductive lines and spaces between theconductive lines, while the substrate is in the plasma processingchamber, wherein the conductive lines have a width and the spacesbetween the conductive line have widths, wherein the widths of thespaces between the conductive lines is less than the widths of the maskspaces, and wherein the widths of the conductive lines is greater thanthe widths of the line masks.
 23. The method, as recited in claim 22,wherein a ratio of the widths of the mask lines to the widths of themask spaces is less than 1:1 and wherein a ratio of the widths of theconductive lines to the widths of the spaces between the conductivelines is not less than 1:1.
 24. The method, as recited in claim 22,wherein a ratio of the widths of the mask lines to the widths of themask spaces is less than 1:1 and wherein a ratio of the widths of theconductive lines to the widths of the spaces between the conductivelines is greater than 1:1.
 25. The method, as recited in claim 22,wherein the widths of the mask spaces is more than 50% greater than thewidths of the spaces between the conductive lines.
 26. The method, asrecited in claim 22, further comprising etching the conformal layer witha first etch recipe, wherein the etching of the conductive layer uses asecond etch recipe, which is different than the first etch recipe.
 27. Asemiconductor device formed by the method of claim
 22. 28. The method,as recited in claim 22, further comprising stripping the conformal layerand mask with a single stripping step, while the substrate is in theplasma processing chamber.
 29. The method, as recited in claim 22,wherein the first deposition and second deposition are alternated for atleast 6 cycles.